1. Field of the Invention
This invention relates to an optical scanning device to be used as reading or recording means for an image.
2. Description of the Prior Art
Heretofore, such optical scanning devices have been widely used in various fields, the scanning capability of which have been remarkably improved to meet various demands arising from the fields concerned. In view of a recent trend that the scanning devices are in most cases incorporated as a component element in systematized information processing apparatus such as terminal devices, etc., its miniaturization has been strongly desired.
For miniaturization of these devices, there can be contemplated various methods. One such method is to reduce the size of the scanning focussing lens system. However, reduction in number of the lens group consisting of the focussing lens system causes reduction in freedom of designing, correction in aberration, and introduces various other problems. One such problem resides in scanning a surface to be scanned at a constant speed.
For scanning the surface to be scanned at a constant speed, there have so far been known various prior arts. For example, U.S. Pat. No. 3,687,025 teaches scanning of a surface to be scanned at a constant speed by a scanning lens consisting of 4-lens construction, and U.S. Pat. No. 3,946,150 discloses scanning of a surface to be scanned at a constant speed by a scanning lens consisting 3-lens structure. U.S. Pat. No. 4,099,829 shows a structure where a small number of lenses constitutes a scanning lens. In this U.S. Patent, a single scanning lens is used for scanning a surface to be scanned. However, there is no teaching to scan the surface at a constant speed.